You can turn off the Share from Finder Preferences>Sidebar>Shared by unchecking boxes.
This will hide from you the offending PC so you do not have to see it anymore.
If you want to get rid of it use the Finder drop down menu>Go>Go to Folder, and copy and paste:
from there delete these two plist files:
Relaunch the Finder- by control-option key on the Finder Dock icon (far left of the Dock.) You may have to customize you sidebar with personal folders etc after relaunch.
If you can not locate those two plist then Go to Folder with the complete string ex.